Dielectric ceramic composition for high frequency wave

ABSTRACT

A dielectric ceramic composition for high frequency wave having a composition comprising Al, Zr, Ti, Sn and O as a basic composition and represented by compositional formula: 
     
       
           a Al 2 O 3 - b ZrO 2 - c TiO 2 - d SnO 2    
       
     
     (in which 0.4068&lt;a&lt;0.9550, 0&lt;b&lt;0.1483, 0.0225&lt;c&lt;0.3263, 0.0203&lt;d&lt;0.1186, a+b+c+d=1).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dielectric ceramic composition for highfrequency wave having a specific dielectric constant ε_(r) of 10 to 20,and less dielectric loss tan δ in a high frequency wave region, andcapable of easily controlling temperature coefficient τ_(f) at theresonant frequency (f₀)

2. Description of the Related Art

With the rapid progress of communication networks in recent years,frequencies used for communication have been extended and reached highfrequency wave regions such as microwave regions or milli-wave regions.The size of the microwave circuits or milli-wave circuits can beminiaturized as a specific dielectric constant ε_(r) is larger. However,if the specific dielectric constant ε_(r) is excessively large, thefabrication accuracy is lowered regarding the high frequency regionhigher than the microwave region. Therefore, materials having relativelysmall specific dielectric constant ε_(r) are necessary.

As the dielectric ceramic composition of this type, for example,BaO—MgO—WO₃ series materials (Japanese Patent Laid-Open No. 236708/1994)and Al₂O₃—TiO₂—Ta₂O₅ series material (Japanese Patent Laid-Open52760/1997) have been proposed. However, they are not yet sufficientregarding the characteristics as the high frequency wave use and, adielectric ceramic composition having further excellent characteristicshas been demanded. Furthermore, from the point of mass production, lessscattering of the characteristic against firing temperature fluctuationis requested.

Meanwhile, alumina (Al₂O₃) exhibits satisfactory dielectriccharacteristics having a specific dielectric constant ε_(r) of 9.8 andtan δ of 3 to 5×10⁻⁵ at a measuring frequency of 10 GHz but since thetemperature coefficient τ_(f) at the resonance frequency (f₀) is −55ppm/° C., the application use is restricted. Further, the firingtemperature of Al₂O₃ is as high as 1600° C. or higher to result in aproblem that the cost for the firing step is increased.

SUMMARY OF THE INVENTION

This invention intends to eliminate the problems described above andprovide a dielectric ceramic composition for high frequency wave havinga specific dielectric constant ε_(r) of 10 to 20 and dielectric lossless tan δ, which is less scattering, and the absolute value of atemperature coefficient τ_(f) at the resonance frequency (f₀) of 30ppm/° C. or less, which can easily be controlled.

This invention relates to a dielectric ceramic composition for highfrequency wave having a composition comprising, Al, Zr, Ti, Sn, and O asa basic component and represented by the compositional formula:

aAl₂O₃-bZrO₂-cTiO₂-dSnO₂

(in which 0.4068<a<0.9550, 0<b<0.1483, 0.0225<c<0.3263, 0.0203<d<0.1186,a+b+c+d=1).

This invention can provide a dielectric ceramic composition for highfrequency wave having a specific dielectric constant ε_(r) of 10 to 20and less dielectric loss tan δ in a high frequency wave region, which isless scattering against firing temperature fluctuation, and capable ofeasily controlling a temperature coefficient τ_(f) at the resonantfrequency (f₀).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray diffraction chart for a dielectric ceramiccomposition according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

The grounds for limitations imposed on the composition of this inventionwill be explained. In the dielectric ceramic composition for highfrequency wave having a composition comprising aluminum, zirconium,titanium, tin and oxygen as a basic component and represented by thecompositional formula:

aAl₂O₃-bZrO₂-cTiO₂-dSnO₂

when a is 0.4068 or less, tan δ of the dielectric body increases and, onthe contrary, when it is 0.9550 or more, the absolute value for thetemperature coefficient τ_(f) at the resonance frequency f₀ exceeds 30ppm/° C. which is not preferred. Further, incorporation of Zr decreasestan δ and decreases scattering of the characteristic tan δ againstfiring temperature fluctuation. However, if b is 0.1483 or more, tan δincreases undesirably. Further, when c is 0.0225 or less, the absolutevalue for the temperature coefficient τ_(f) at the resonance frequencyf₀ exceeds 30 ppm/° C. and, on the other hand, when it is 0.3263 ormore, tan δ increases remarkably which is not preferred. Further, when dis 0.0203 or less, the absolute value for the temperature coefficientτ_(f) at the resonance frequency f₀ exceeds 30 ppm/° C. and, on thecontrary, when it is 0.1186 or more, tan δ increases remarkably which isnot preferred.

Further, in this invention, for obtaining suitable dielectriccharacteristics, it is preferred to incorporate Ta₂O₅ and/or NiO as theauxiliary component. Tan δ increases when the content of Ta₂O₅ isexcessively high, so that the weight ratio e of Ta₂O₅ relative to thebasic component is preferably: 0<e<0.05. Further, since tan δ increaseswhen the content of NiO is excessively high, the weight ratio f of NiOrelative to the basic component is preferably: 0<f<0.05. Particularly,by the combined use of Ta₂O₅ and NiO, scattering of the characteristicscan be decreased and a dielectric ceramic composition for high frequencywave having further smaller tan δ can be obtained.

An example of a suitable process for producing a dielectric ceramiccomposition for high frequency wave according to this invention is shownbelow. Starting materials comprising aluminum oxide, zirconium oxide,titanium oxide and tin oxide, as well as tantalum oxide and nickel oxideas the auxiliary component are wet-mixed each by a predetermined amounttogether with a water and a solvent such as alcohol. Successively, afterremoving water and alcohol, they were pulverized. Successively, anorganic binder such as polyvinyl alcohol is mixed to the thus obtainedpowder into a homogeneous state, which was dried, pulverized and pressmolded (at a pressure of about 100 to 1000 kg/cm²). The dielectricceramic composition represented by the compositional formula describedpreviously can be obtained by firing the resultant molding product at1400 to 1600° C. in an oxygen-containing gas atmosphere such as air.

The thus obtained dielectric ceramic composition can be utilized as thematerial for dielectric resonator, dielectric substrate and laminatedevices by being fabricated into an appropriate shape and size, orsheeted by a doctor blade method or laminated with a sheet and anelectrode.

As the starting materials for aluminum, zirconium, titanium, tin,tantalum and nickel, there can be used Al₂O₃, ZrO₂, TiO₂, SnO₂, Ta₂O₅,and NiO, as well as nitrate, carbonate, hydroxide, chloride and organicmetal compounds, which are converted into oxides upon firing.

EXAMPLE 1

A starting material powder comprising 0.6762 mol of Al₂O₃, 0.0810 mol ofZrO₂, 0.1781 mol of TiO₂ and 0.0648 mol of SnO₂ as the main componentand Ta₂O₅ at a weight ratio of 0.02 to the basic component as theauxiliary component and NiO at a weight ratio of 0.01 relative to thebasic component as the auxiliary component were placed together withethanol and ZrO₂ balls in a ball mill, and wet mixed for 24 hours. Afterremoving the solvent from the solution, they were pulverized.Successively, after adding an appropriate amount of a polyvinyl alcoholsolution to the pulverizates and drying, they were molded into a pelletof 11 mm diameter and 6 mm thickness and fired in an air atmosphere at1525° C. for 4 hours.

After fabricating the ceramic composition of Example 1 thus obtainedinto a size of 9.5 mm diameter and 4 mm thickness, it was measured by adielectric resonance method to determine tan δ at a resonance frequencyof 8 to 10 GHz, specific dielectric constant ε_(r), and temperaturecoefficient τ_(f) at the resonance frequency. The results are shown inTable 2. As seen in Table 2, preferable results were obtained like thatspecific dielectric constant ε_(r) is about 10-20, dielectric loss tan δat a resonance frequency of 8 to 10 GHz is very small such as 2.8×10⁻⁵,and absolute value of temperature coefficient τ_(f) at the resonancefrequency is about 20.

When X-ray diffractiometry was conducted for the resultant dielectricceramic composition, it has been found that α-Al₂O₃ andZr_(0.75)Ti_(0.75)Sn_(0.5)O₄ were mainly formed. FIG. 1 shows the X-raydiffraction chart.

EXAMPLES 2 TO 5

Al₂O₃, ZrO₂, TiO₂ and SnO₂ as the basic component and Ta₂O₅ and NiO asthe auxiliary component were mixed at the ratio shown in Table 1 below,molded under the same conditions as in Example 1, and fired in air at1525° C. for 4 hours to prepare dielectric ceramics. The characteristicsof the resulting ceramics were evaluated by the same method as inExample 1. The results are shown in Table 2.

EXAMPLES 6a TO 6g

Al₂O₃, ZrO₂, TiO₂ and SnO₂ as the basic component and Ta₂O₅ and NiO asthe auxiliary component were mixed at the ratio shown in Table 1 below,molded under the same conditions as in Example 1, and fired in air atthe temperature listed in Table 2 for 4 hours to prepare dielectricceramics. The characteristics of the resulting ceramics were evaluatedby the same method as in Example 1. The results are shown in Table 2. Asseen from Table 2, dielectric loss tan δ is small and less scatteringagainst firing temperature change, so that this dielectric ceramics iseasy for the production.

EXAMPLES 7 TO 11

Al₂O₃, ZrO₂, TiO₂ and SnO₂ as the basic component were mixed without theauxiliary component at the ratio shown in Table 1 below, molded underthe same conditions as in Example 1, and fired in air at 1525° C. for 4hours to prepare dielectric ceramics. The characteristics of theresulting ceramics were evaluated by the same method as in Example 1.The results are shown in Table 2.

COMPARATIVE EXAMPLES 1 TO 2

Al₂O₃, ZrO₂, TiO₂ and SnO₂ as the basic component and Ta₂O₅ and NiO asthe auxiliary component were mixed at the ratio shown in Table 1 below,molded, and fired in air at the temperature listed in Table 2 for 4hours to prepare dielectric ceramics. The characteristics of theresulting ceramics were evaluated by the same method as in Example 1.The results are shown in Table 2. Dielectric loss tan δ at a resonancefrequency of 8 to 10 GHz or absolute value of temperature coefficientτ_(f) at the resonance frequency is large when the composition is out ofthe range of this invention.

COMPARATIVE EXAMPLES 3a TO 3e

Al₂O₃, TiO₂ and SnO₂ without ZrO₂ as the basic component and Ta₂O₅ andNiO as the auxiliary component were mixed at the ratio shown in Table 1below, molded under the same conditions as in Example 1, and fired inair at the temperature listed in Table 2 for 4 hours to preparedielectric ceramics. The characteristics of the resulting ceramics wereevaluated by the same method as in Example 1. The results are shown inTable 2. As seen from Table 2, dielectric loss tan δ scatters muchagainst firing temperature change, so that this dielectric ceramics isdifficult for the production.

TABLE 1 Auxiliary Main component component (molar ratio) (wt %) Al₂O₃ZrO₂ TiO₂ SnO₂ Ta₂O₅ NiO Example 1 0.6762 0.0810 0.1781 0.0648 2 1Example 2 0.6222 0.0945 0.2078 0.0756 2 1 Example 3 0.7316 0.0671 0.14760.0537 2 1 Example 4 0.8111 0.0094 0.0945 0.0850 2 1 Example 5 0.84460.0078 0.0777 0.0699 2 1 Example 6 0.7778 0.0111 0.1111 0.1000 2 1Example 7 0.6762 0.0810 0.1781 0.0648 0 0 Example 8 0.6222 0.0945 0.20780.0756 0 0 Example 9 0.7316 0.0671 0.1476 0.0537 0 0 Example 10 0.77780.0111 0.1111 0.1000 0 0 Example 11 0.8111 0.0094 0.0945 0.0850 0 0Comparative 0.4068 0.1483 0.3263 0.1186 2 1 Example 1 Comparative 0.95500.0022 0.0225 0.0203 2 1 Example 2 Comparative 0.7280 0.0000 0.16600.1060 2 1 Example 3

TABLE 2 Dielectric characteristic Firing ε_(r) tan δ (×10⁻⁵) τ f(ppm/°C.) Temperature Example 1 14.6 2.8 −20.2 1525° C. Example 2 13.7 2.8−20.2 1525° C. Example 3 15.3 4.1 −25.5 1525° C. Example 4 12.4 4.9 −8.41525° C. Example 5 12.0 5.1 −26.7 1525° C. Example 6a 13.2 4.7 −1.11450° C. Example 6b 13.2 4.3 −1.9 1475° C. Example 6c 13.2 4.7 −2.01500° C. Example 6d 13.2 4.8 −2.2 1525° C. Example 6e 13.1 4.9 −2.21550° C. Example 6f 13.1 4.4 −2.0 1575° C. Example 6g 13.1 4.6 −2.01600° C. Example 7 14.0 4.1 −22.4 1525° C. Example 8 13.6 3.2 −21.51525° C. Example 9 14.9 4.1 −27.2 1525° C. Example 10 13.0 5.7 −2.01525° C. Example 11 12.2 6.3 −9.5 1525° C. Comparative 18.2 14.1  −43.31500° C. Example 1 Comparative 10.1 2.8 −49.4 1575° C. Example 2Comparative 12.1 9.8 −9.0 1450° C. Example 3a Comparative 12.9 7.4 −9.01475° C. Example 3b Comparative 13.5 7.1 −9.4 1500° C. Example 3cComparative 13.5 6.9 −10.4 1525° C. Example 3d Comparative 13.3 8.1−10.8 1550° C. Example 3e

What is claimed is:
 1. A dielectric ceramic composition for highfrequency wave having a composition comprising Al, Zr, Ti, Sn and O as abasic component and represented by the compositional formula:aAl₂O₃-bZrO₂-cTiO₂-dSnO₂ (in which 0.4068<a<0.9550, 0<b<0.1483,0.0225<c<0.3263, 0.0203<d<0.1186 and a+b+c+d+=1).
 2. The dielectriccomposition for high frequency wave according to claim 1, which containsTa₂O₅ as an auxiliary component and the ratio e of Ta₂O₅ relative tosaid basic component is: 0<e<0.05.
 3. The dielectric composition forhigh frequency wave according to claim 2 which contains NiO as anauxiliary component and the ratio f of NiO relative to said basiccomponent is: 0<f<0.005.
 4. The dielectric composition for highfrequency wave according to claim 1 which contains NiO as an auxiliarycomponent and the ratio f of NiO relative to said basic component is:0<f<0.05.